Reduction of cross-talks between circuit and sensor layer in the Kyoto's X-ray astronomy SOI pixel sensors with Double-SOI wafer

We have been developing silicon-on-insulator pixel sensors, “XRPIXs,” for future X-ray astronomy satellites. XRPIXs are equipped with a function of “event-driven readout,” with which we can read out only hit pixels by trigger signals and hence realize good time resolution reaching ∼10μs. The current version of XRPIX suffers from a problem that the spectral performance degrades in the event-driven readout mode compared to the frame-readout mode, in which all the pixels are read out serially. Previous studies have clarified that one of the causes is capacitive coupling between the sense node and the trigger signal line in the circuit layer. In order to solve the problem, we adopt the Double SOI structure having a middle silicon layer between the circuit and the sensor layers. We expect the middle silicon layer to work as an electrostatic shield and reduces the capacitive coupling. In this paper, we report the spectroscopic performance of XRPIX with the middle silicon layer. We successfully reduce the capacitive coupling and the readout noise.